Hints &amp; Tips for Optimizing Linux Disk Usage

It seems that no matter how much hard disk storage you have, it quickly becomes full. Because Linux is free, many users are on a limited budget and can't afford to simply buy more hardware. This article describes some simple techniques for making the best use of the disk storage you have now.

Half Full or Half Empty?

The first question to be answered is, how full is your disk?
The best way to do this is with the “df” command. This is what my
system shows:

In this case I have slightly more that 16 megabytes available
on my single 94 megabyte partition, making it 82% full. If you have
multiple disk partitions and/or drives, you will see a entry in the
listing for each mounted partition.

You may think that as long as you are under 100%, everything
is fine. This is not the case, for several reasons.

First, you need some space in reserve for temporary files.
Compiling, for example, requires that various intermediate files be
stored in a temporary directory. If you don't have enough space for
these files, the command will fail, possibly in strange ways. A
normal user could even bring the system down by filling up the root
disk.

Second, once your disk approaches full capacity, performance
starts to degrade. The file system has to spend more time looking
for free blocks on the disk to use. The amount of performance
degradation depends on how full the disk is, and the type of file
system. A good rule of thumb is to keep the disk below 80% full if
possible, and definitely below 90%.

Load Balancing

You may have multiple disk drives, and you may have divided
one or more drives into separate partitions. This is one way, for
example, to avoid having the root partition filled by user data.
The disadvantage is that you may find that one partition is full,
even though others have space available.

If this is the case, one option is to repartition the drives
to better balance the load. This will require backing up all your
data first, since repartitioning is destructive.

A second choice is to move some of the files from one
partition or disk to another. Using symbolic links, you may be able
to do this without affecting other applications.

You likely have at least one swap partition. Choosing its
size is a tradeoff between having adequate swap space and losing
valuable filesystem space. If you find you have more swap space
than needed (the “free” command is useful here), the n you can
consider repartitioning to make the swap partition smaller. If you
only rarely require a lot of swap space (e.g. during large
compiles) an option is to use a smaller swap partition, and to add
a swap file on those occasions when extra swap is needed.

If your drives are load balanced and disk space is still a
problem, or if you have a single partition, then you are ready for
the techniques described in the rest of this article.

Finding the Big Files

A useful concept is the Pareto or 80/20 principle. Applied
here, it says that 80% of the disk space is contained in 20% of the
files (more or less). How do you find this 20%? One tool is the
“find” command. The following command line, for example, will find
all of the files on the system that are larger than 1 million bytes
(you may have to run this as root so you have access to all the
directories; expect it to take a while to run, depending on disk
size):

% find / -size+1000000c -ls

This command tells find to locate any file larger than 1
million characters and printing out its directory information. If
you are not familiar with the find command, read up on i t in the
man page. It can be a useful tool for identifying areas to
attack.

Removing Files

The obvious solution to freeing up disk space is to delete
files. With some detective work, you may find a lot of baggage on
your system that you don't need. First though, two important
warnings:

Make sure you have backups of everything you are
deleting, in case you find out later you really needed it.

Have an emergency floppy that you can boot from
(e.g. the SLS A1 disk) in case you delete something (like
/vmlinuz?) that puts your system in an unbootable state.

On an SLS or Slackware system, it is easy to identify and
remove software packages. Review the packages that you have
installed, see how much disk space they require, and delete the
ones you don't need.

Some of the things that can save a lot of space if they are
not needed are:

networking, including NFS and uucp

newsreaders (tin, trn, cnews, etc...)

language tools: p2c, f2c, lisp, smalltalk

TeX and LaTeX

source code

You can remove the nroff source for the man pages (in
/usr/man/man?) and keep only the compressed, formatted pages (in
/usr/man/cat?). Make sure all man pages have been formatted
first.

The full distribution of emacs lisp source files (*.el) is
quite large. You can just keep the byte compiled (*.elc)
files.

If you have compiled the Linux kernel, remove the object
files (e.g. cd /usr/src/linux ; make clean).

You may have accumulated some old libraries in /lib and
/usr/lib. Some binaries may still require them though. You may be
able to determine whether they are used by running ldd on your
binaries. This is one area I suggest you avoid unless you know what
you are doing, because you can easily cause your system to break if
you delete needed libraries.

If you run the X window system, the font files take a lot of
disk space (they are usually in /usr/lib/X11). Make sure the .pcf
font files are compressed. You may be able to delete some of the
more obscure fonts as well. If you compress or delete any fonts, be
sure to run the mkfontdir command afterward.

I found on my system that there were a number of duplicate
files in /bin and /usr/bin. Eliminating duplicates can save space,
but watch that you are not just deleting links to the same file.
The diff command is useful here for comparing director of files
(e.g. diff /bin /usr/bin).

Certain files grow without limit and should be periodically
purged. These include:

/etc/wtmp
/etc/ftmp
/var/log/notice

In general you should truncate these files to zero length
(e.g., cp /dev/null /var/log/notice) rather than deleting the
files, or the programs that use them may not create new
files.

Finally, there may be files that you need periodically but do
not need on-line all the time (e.g. the Linux kernel source).
Consider backing these up to floppy or tape and restoring them on
an as-needed basis.

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